Materials which are used to shield and enclose various sensitive components in electronic devices generally must possess a high degree of electrical insulating capacity, while also possessing a high level of flame retardancy. For instance, such materials ideally have an arc track resistance greater than 90 seconds, and a surface resistivity greater than 10.sup.9 ohms per square mil, while also having a flame resistance rating (UL 94) of V-0 when such a material has a thickness of about 5 mils to about 250 mils. Materials which have superior electrical insulating properties but inferior flame resistant properties, ad vice versa, are not acceptable for some end uses. An additional problem compicating the search for a material having both of the above-described properties arises when a particular additive enhances one property while detracting from the other. For example, halogen compounds added to a thermoplastic composition may improve the flame resistance of the material but may also decrease the arc track resistance of the material.
Prior art materials used to shield such components include fibrous substances such as asbestos. However the use of these materials creates other problems because such fibers are both carcinogenic and toxid by inhalation. Other prior art materials, such as those formed from aramid fibers, may provide a degree of flame resistance and elecrical insulation, but are very expensive, and often lack dimensional stability because of moisture absorption. Furthermore, such materials generally cannot be thermoformed into various shapes.